Every new born being indeed comes fresh and blithe into the new existence, and enjoys it as a free gift: but there is, and can be, nothing freely given. It's fresh existence is paid for by the old age and death of a worn out existence which has perished, but which contained the indestructible seed out of which the new existence has arisen: they are one being.
The traits the word 'childish' addresses are seen so often in adults that we should abolish this age-discriminatory word when it comes to criticizing behavior associated with irresponsibility and irrational thinking.